The goal of this project is to develop novel oxytocin (OXT) analogues with improved safety and efficacy vs. native OXT for the treatment of obesity and related metabolic disorders. Obesity is an increasing health-care burden in the US and, even though it is recognized as a significant risk factor for developing cardiovascular disease and type-2 diabetes, there has been limited progress in developing safe and effective methods for reducing body weight. Diet and exercise have proven ineffective for most patients while eligibility criteria for bariatric surgery limits its? use to only the most obese individuals. The use of pharmacotherapy to treat obesity has also been challenging due to limited efficacy and significant safety concerns, including serious behavioral and cardiovascular side effects, which have limited their clinical use. OXT is a downstream target of the adiposity signal leptin. OXT is an attractive therapeutic target to treat obesity in humans because it reduces body weight in diet-induced obese (DIO) rodents even in the face of an impaired ability of leptin to reduce food intake. Moreover, we recently translated these effects to DIO nonhuman primates and determined that OXT induces weight loss via combined effects of reducing food intake and increasing energy expenditure. Numerous studies in animal models and humans have demonstrated that activation of the OXT receptor (OXTR) effectively reduces body weight through multiple mechanisms, including increased satiety, energy expenditure, and improved lipid metabolism. Nevertheless, OXT and its published analogues exhibit poor metabolic stability resulting in short plasma half-life, potential to induce off-target toxicity via vasopressin family of receptors, and sub-optimal OXTR agonistic activity. With the proposed studies, we aim to target the OXT signaling pathway using novel selective, potent and metabolically stable OXT analogues with the goal to develop a pharmacotherapy for safe and effective obesity intervention. We already have developed a series of novel molecules with significantly improved metabolic stability and comparable or better activity at OXTR. Preliminary in vivo studies support the significant potential of these analogues as weight-loss agents. We now propose to further characterize our analogues in vitro potency against OXTR (i.e.,activation of Gq, Gi and Go) and selectivity versus vasopressin V1a/b and V2 receptors in cell-based reporter assays (Aim 1). Promising agents will be evaluated for their minimum effective and maximum tolerated doses in Sprague- Dawley rats as well as their in vivo pharmacokinetic properties. One champion OXT analogue will be further evaluated in DIO rats during longer 21-d treatment on changes of body weight, food intake, inflammatory and metabolic parameters, and measures of energy homeostasis (Aim 2). After completion of these studies, several lead molecules will be evaluated for detailed pharmacokinetics, biodistribution (i.e., CNS penetration), preclinical toxicology, and long-term efficacy (DIO and genetic obesity models) in a phase-II STTR grant that will position us to conduct an Investigational New Drug application and prepare for clinical trials.